1. Field of the Invention
This invention relates to a base structure or a boring machine of a type adapted to bore upwardly from an underground location. More particularly, it relates to a base structure adapted to permit azimuthal adjustment of the boring line. It also relates to a method for establishing the boring line of an overhead boring machine.
2. Description of the Prior Art
Machines for mechanically boring a hole or tunnel upwardly through an earth formation from an underground location are well-known. Examples of such known machines are disclosed in U.S. Pats. No. 3,304,033, granted Feb. 14, 1967 to R. L. Thompson; U.S, Pat. No. 3,490,546, granted Jan. 20, 1970 to J. S. Hattrup et al.; U.S. Pat. No. 3,604,754, granted Sept. 14, 1971 to G. Kampf-Emden Hosel et al; U.S. Pat. No. 3,780,815, granted Dec. 25, 1973 to C. D. Barron et al. and U.S. Pat. No. 3,840,272, granted Oct. 8, 1974 to C. H. Crane et al.
The machines disclosed by the above patents are supported on base structures which are rigidly affixed to the ground surface of the underground location. The machines are pivotally mounted to their base structures in such a manner that the machines can be tilted at any angle along a 90.degree. vertical arc of circle to establish a drilling line. A distinct disadvantage of such mounting arrangement is that the drilling line generally cannot vary outside of a single 90.degree. arc of vertical circle once the base is assembled on the tunnel floor. Some base structures also enable a second arc of vertical circle, perpendicular to the first, to be established. Nevertheless, the azimuthal position of the boring machine's drilling line must be selected ahead of time so that the base assembly may be positioned on the ground surface accordingly. If the base assembly is misaligned, or if a change in the azimuthal position of the drilling line is desired after the base assembly has been emplaced, the entire assembly must either be taken apart and moved, or a new base structure assembled. Such a process is both time-consuming and costly.